wordpress featured image from external url without download

i would like to use external pictures as featured image on wordpress.

either changing worpdress code. (adding a fetured image metabox accepting urls and do some modifications in order to display the featured image from url correctly)

or modifiying the plugin WP remote thumbnail, which set a featured image from an image url. it download the picture and create thumbnails in wordpress and set the featured image.

modifications:
* no download from the url, just use the url to display directly on the blog.
* remove wp-content/uploads from the url generated by wordpress to display featured image (only for external urls)
* no thumbnails creation.

thank you very much for reading
i know there is a lot of questions about this problem
but if we solve this question it could be useful for a lot of ppl.

here the code:

<?php
/*
Plugin Name: WP Remote Thumbnail
Plugin URI: http://magnigenie.com/wp-remote-thumbnail-set-external-images-featured-image/
Description: A small light weight plugin to set external/remote images as post thumbnail/featured image.
Version: 1.0
Author: Nirmal Kumar Ram
Author URI: http://magnigenie.com
License: GPLv2 or later
License URI: http://www.gnu.org/licenses/gpl-2.0.html
*/
?>
<?php

/**
 * Initialize wprthumb on the post edit screen.
 */
function init_wprthumb() {
    new wprthumb();
}

if ( is_admin() ) {
    add_action( 'load-post.php', 'init_wprthumb' );
    add_action( 'load-post-new.php', 'init_wprthumb' );
}


class wprthumb {

    /**
     * Hook into the appropriate actions when the wprthumb is constructed.
     */
    public function __construct() {
        add_action( 'add_meta_boxes', array( $this, 'add_meta_box' ) );
        add_action( 'save_post', array( $this, 'save' ) );
    }

    /**
     * Adds the meta box container.
     */
    public function add_meta_box( $post_type ) {
    if ( post_type_supports( $post_type, 'thumbnail' )) {
      add_meta_box(
        'some_meta_box_name'
        ,'Remote Post Thumbnail'
        ,array( $this, 'render_meta_box_content' )
        ,$post_type
        ,'side'
        ,'default'
      );
    }
    }

    /**
     * Save the meta when the post is saved.
     */
    public function save( $post_id ) {

        /*
         * We need to verify this came from the our screen and with proper authorization,
         * because save_post can be triggered at other times.
         */

        // Check if our nonce is set.
        if ( ! isset( $_POST['wprthumb_nonce'] ) )
            return $post_id;

        $nonce = $_POST['wprthumb_nonce'];

        // Verify that the nonce is valid.
        if ( ! wp_verify_nonce( $nonce, 'wprthumb' ) )
            return $post_id;

        // If this is an autosave, our form has not been submitted,
    // so we don't want to do anything.
        if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) 
            return $post_id;

        // Check the user's permissions.
        if ( 'page' == $_POST['post_type'] ) {

            if ( ! current_user_can( 'edit_page', $post_id ) )
                return $post_id;

        } else {

            if ( ! current_user_can( 'edit_post', $post_id ) )
                return $post_id;
        }

    /* All good, its safe for us to save the data now. */

        // Sanitize the user input.
        $image = sanitize_text_field( $_POST['remote_thumb'] );
    $upload_dir = wp_upload_dir();
    //Get the remote image and save to uploads directory
    $img_name = time().'_'.basename( $image );
    $img = wp_remote_get( $image );
    $img = wp_remote_retrieve_body( $img );
    $fp = fopen( $upload_dir['path'].'/'.$img_name , 'w');
    fwrite($fp, $img);
    fclose($fp);

    $wp_filetype = wp_check_filetype( $image , null );
    $attachment = array(
      'post_mime_type' => $wp_filetype['type'],
      'post_title' => preg_replace('/.[^.]+$/', '', $image ),
      'post_content' => '',
      'post_status' => 'inherit'
    );

    //require for wp_generate_attachment_metadata which generates image related meta-data also creates thumbs
    require_once( ABSPATH . 'wp-admin/includes/image.php' );
    $attach_id = wp_insert_attachment( $attachment, $image, $post_id );
    //Generate post thumbnail of different sizes.
    $attach_data = wp_generate_attachment_metadata( $attach_id , $image );
    wp_update_attachment_metadata( $attach_id,  $attach_data );
    //Set as featured image.
    delete_post_meta( $post_id, '_thumbnail_id' );
    add_post_meta( $post_id , '_thumbnail_id' , $attach_id, true);
    }

    /**
     * Render Meta Box content.
     */
    public function render_meta_box_content( $post ) {

        // Add an nonce field so we can check for it later.
        wp_nonce_field( 'wprthumb', 'wprthumb_nonce' );

        // Display the form, using the current value.
        echo '<label for="remote_thumb">';
        _e( 'Enter remote image url', 'wprthumb' );
        echo '</label> ';
        echo '<input type="text" id="remote_thumb" name="remote_thumb" size="25" />';
    }
}